Synthetic resins such as polyesters, polyamides and polycarbonates are used as materials that constitute, for example, electrical and electronic devices such as personal computers, printers and copying machines; home electric appliances such as televisions and refrigerators; packaging materials such as containers and packages; building materials such as wall and flooring materials; and automobile interior and exterior materials. These synthetic resins have excellent moldability, productivity and mechanical properties; however, since they are produced using petroleum as raw material, when they are disposed in nature, their low decomposability imposes a large stress to the environment such as soil. In addition, incineration of these synthetic resins leads to generation of carbon dioxide and thus presents a problem from the standpoint of preventing global warming.
On the other hand, plant-derived resins have excellent biodegradability and thus do not put much stress to the soil environment. In addition, since these resins are, in the first place, synthesized by photosynthetic reaction performed by plants using carbon dioxide and water in the atmosphere as raw materials, even if they are incinerated and carbon dioxide is consequently generated, the balance of carbon dioxide in the atmosphere stays even; therefore, these plant-derived resins are regarded as so-called “carbon-neutral” materials. From the standpoint of preventing global warming, it is urgent to replace petroleum-derived resins with such carbon-neutral plant-derived resins.
As a plant-derived resin, a cellulose derivative has been utilized. For example, as film materials, cellulose esters such as cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate phthalate have been conventionally used.
However, these cellulose derivatives such as cellulose esters have poor moldability by themselves and they also have a problem in terms of the processability. Thus, when these cellulose derivatives are thermally molded by injection molding or the like, it is necessary to add a plasticizer thereto. In addition, since the cellulose esters are colored during processing and molding, there is a problem in terms of the color tone of a molded article obtained therefrom.
It has been proposed to add a phosphate as the plasticizer (Patent Documents 1 and 2). However, the processability and the moldability are largely different depending on kinds of phosphates, and satisfactory performance has not been attained. In addition, it is considered necessary to solve the coloration problem. Furthermore, there is still room for improvement with respect to the heat resistance.
On another front, as molding materials to be used in place of petroleum-derived resins, cellulose derivatives such as cellulose esters are demanded to have flame retardancy as well.